Publications
Drag in Bose-Fermi mixtures
We use kinetic theory to model the dynamics of a small Bose condensed cloud of heavy particles moving through a larger degenerate Fermi gas of light particles. Varying the Bose-Fermi interaction, we find a crossover between bulk- and surface-dominated regimes - where scattering occurs throughout the Bose cloud or solely on the surface, respectively. We calculate the damping and frequency shift of the dipole mode in a harmonic trap as a function of the magnetic field controlling an interspecies Feshbach resonance.
Fragility of surface states in topological superfluid 3He
Superfluid 3He, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust.
Effect of the density of states at the Fermi level on defect free energies and superconductivity: A case study of Nb3Sn
Although often ignored in first-principles studies of material behavior, electronic free energy can have a profound effect in systems with a high-temperature threshold for kinetics and a high Fermi-level density of states (DOS). Nb3Sn and many other members of the technologically important A15 class of superconductors meet these criteria. This is no coincidence: both electronic free energy and superconducting transition temperature Tc are closely linked to the electronic density of states at the Fermi level.
The marvels of moiré materials
Note on generalized symmetries, gapless excitations, generalized symmetry protected topological states, and anomaly
We consider quantum many body systems with generalized symmetries, such as the higher form symmetries introduced recently, and the 'tensor symmetry'. We consider a general form of lattice Hamiltonians which allow a certain level of nonlocality. Based on the assumption of dual generalized symmetries, we explicitly construct low energy excited states. We also derive the 't Hooft anomaly for the general Hamiltonians after 'gauging' the dual generalized symmetries.
Starting dynamics of a linear-cavity femtosecond Mamyshev oscillator
Mamyshev oscillators can generate high-power femtosecond pulses, but starting a mode-locked state has remained a major challenge due to the suppression of continuous-wave lasing. Here, we study the starting dynamics of a linear Mamyshev oscillator designed to generate high-power femtosecond pulses while avoiding component damage. Reliable starting to stable mode-locking is achieved with a combination of modulation of the pump power and shifting of a filter passband. The starting process is automated, with full electronic control.
Utilizing complex oxide substrates to control carrier concentration in large-area monolayer MoS2films
Bandgap engineering is central to the design of heterojunction devices. For heterojunctions involving monolayer-thick materials like MoS2, the carrier concentration of the atomically thin film can vary significantly depending on the amount of charge transfer between MoS2 and the substrate. This makes substrates with a range of charge neutrality levels - as is the case for complex oxide substrates - a powerful addition to electrostatic gating or chemical doping to control the doping of overlying MoS2 layers.
Lack of Simple Correlation between Switching Current Density and Spin-Orbit-Torque Efficiency of Perpendicularly Magnetized Spin-Current-Generator–Ferromagnet Heterostructures
Spin-orbit torque can drive electrical switching of magnetic layers. Here, we report that, at least for micrometer-sized samples, there is no simple correlation between the efficiency of dampinglike spin-orbit torque (ζDLj) and the critical switching current density of perpendicularly magnetized spin-current generator-ferromagnet heterostructures.
Physics of symmetry protected topological phases involving higher symmetries and its applications
We discuss physical constructions and the boundary properties of various symmetry-protected topological phases that involve 1-form symmetries from one spatial dimension to four spatial dimensions (4d). For example, the prototype three-dimensional (3d) boundary state of 4d SPT states involving 1-form symmetries can be either a gapless photon phase (quantum electrodynamics) or gapped topological order enriched by 1-form symmetries; that is, the loop excitations of these topological orders carry nontrivial 1-form symmetry charges.
Reaction rates and the noisy saddle-node bifurcation: Renormalization group for barrier crossing
Barrier crossing calculations in chemical reaction-rate theory typically assume that the barrier is large compared to the temperature. When the barrier vanishes, however, there is a qualitative change in behavior. Instead of crossing a barrier, particles slide down a sloping potential. We formulate a renormalization group description of this noisy saddle-node transition. We derive the universal scaling behavior and corrections to scaling for the mean escape time in overdamped systems with arbitrary barrier height.